This disclosure relates to a whirling tool for machining a workpiece. This disclosure relates in particular to a whirling tool having replaceable cutting plates. This whirling tool is suitable in particular for thread whirling.
Whirling is a metal-cutting manufacturing method which in terms of the tool and in terms of the kinetics represents a special form of screw milling. Whirling serves in particular for producing threads, however can also be generally used for producing rotationally symmetrical parts such as, for example, worms, screws, or rotors.
By virtue of the high performance capability of this metal-cutting manufacturing method, whirling is suitable in particular for machining workpieces from tough materials such as titanium or precious metal. For this reason, the majority of all bone screws today are produced by thread whirling, for example.
It is a characteristic of whirling that both the whirling tool as well as the workpiece are rotated. The whirling tool which determines the cutting speed, orbits in an eccentrically positioned manner at a high rotational speed about the slowly rotating workpiece. The feed rate of the workpiece along the longitudinal axis of the latter is set according to the desired thread pitch to be produced. Moreover, the whirling tool, depending on the desired thread pitch, is pivoted about the x-axis of said whirling tool. The radial infeed of the whirling tool in relation to the workpiece establishes the depth of the thread.
By virtue of the eccentric positioning of the workpiece in relation to the whirling tool, relatively short chips are formed. This has an advantageous effect on the surface quality of the machined workpiece.
A difference is made between external whirling and internal whirling. External whirling typically serves for producing external threads, whereas internal whirling typically serves for producing internal threads. The cutting edges in the case of external whirling are directed inward, wherein the whirling tool rotates about the workpiece. Therefore, external whirling is in some instances also referred to as milling by milling cutting edges with internal teeth. In contrast, the cutting edges in the case of internal whirling are directed outward. The whirling tool herein rotates within a bore of the workpiece. The principle of the eccentric whirling movement of the tool and of the simultaneous movement of the workpiece (both rotating as well as in the longitudinal direction) in the case of external and internal whirling is otherwise identical.
A problem which can be determined in the case of whirling tools is the relatively high wear on the used cutters or cutting edges, respectively. This in many instances leads to relatively short service lives. The cutting plates have to be replaced often in the case of whirling tools having replaceable cutting plates. This in turn ultimately leads to increased production costs.